1. Technical Field
This application relates generally to methods and apparatus for polarizing light. In particular, this application relates to methods and apparatus for converting linear-polarized light into radial-polarized light.
2. The Relevant Technology
Radial polarization of light can produce light that has a tighter focus and thus can achieve an approximately 38% higher resolution than what is considered to be the standard diffraction limit. Radial-polarized light has applications in near-field optics, confocal microscopy devices, atom trapping, optical tweezers, and material processing.
Radial polarization generators are known to convert linear-polarized light into radial-polarized light. For example, in laser applications, radial-polarized laser beams can be focused more tightly than laser beams with other polarization states (such as linear or circular polarizations), leading to finer spatial resolution in any laser-scanning microscopy technique. Additionally, at the focus of radial-polarized laser beams there exists a strong electric-field component along the propagation axis of the laser, the optic axis. Thus, radial-polarized laser beams can be used to preferentially probe particles, such as fluorophores like molecules and quantum dots, which are oriented along this axis among all the particles within a heterogeneous system. In addition, radial-polarized beams are important for nanometer-scale apertureless near-field scanning optical microscopy, where a sharp tip most effectively scatters laser light when it is polarized in the same direction as the tip axis. Using radial-polarized light focused at the tip allows for laser illumination along the tip axis, which enables nanometer-scale resolution.
Present methods and apparatus for producing radial polarized light from linear-polarized light are limited in that they are dependent on the wavelength of the originating light. Moreover, these methods and apparatus can be difficult and expensive to implement and manufacture.